September 2019 CWMN Report

The Neponset River makes a comeback with better E. coli, Phosphorus, and Dissolved Oxygen levels in September.


E. Coli Results

In September, 75% of the sites met the EPA standard for boating, and 63% of the sites met the standard for swimming.  More than 50% of the sites could be considered extremely safe for swimming, falling well below the allowed E. coli level. Below is a map of the watershed containing graduated symbols for each site sampled.  A green symbol indicates E. coli levels safe for swimming, a yellow symbol indicates E. coli levels safe for boating, and  a red symbol indicates E. coli levels exceeding safe standards.

These much-improved numbers are partly thanks to a dry sampling day, meaning less bacteria and pollution is entering the water via storm drains.

We typically see a spike in E.coli bacteria when it rains because of stormwater runoff polluted with dog waste. We recommend staying out of the water for at least 48 hours after any storm.

Water quality in the Neponset River, when it hasn’t rained, is typically similar to what we saw in September, with almost all sites being safe for boating, and many more sites that are also safe for swimming.

Follow this link to a list of CWMN site descriptions: CWMN 2019 Site Descriptions

September E. coli Levels Map

A map showing all CWMN sites sampled in September 2019 with graduating symbols indicating E. coli level according to the legend. 

September E. coli Levels Graph

September data for E. coli levels by CFUs (colony-forming units). The Neponset River saw greatly improved levels of E.coli in the month of September.


Phosphorus Results

Phosphorus is a key nutrient for plants. This is why people add fertilizer to their gardens and yards. Unfortunately, when too much fertilizer is applied it can get washed off when it rains and it ends up in our streams and ponds. Too much phosphorus can cause harmful algal blooms, cyanobacteria blooms, and fish kills.

Only 15 out of 27 streams (55%), and 2 out of 5 ponds tested had levels of phosphorus that are considered healthy.  However, this is an improvement compared to August, which saw only 9% of streams meet healthy Phosphorus levels.

For tips on how to reduce your phosphorus impact on the river visit https://yourcleanwater.org/lawn/

September Phosphorus Graph

September data for Total Phosphorus. The Neponset River experienced better than average Phosphorus levels in September.


Dissolved Oxygen Results

Dissolved Oxygen has been referred to as the “air” fish breathe under water. If the concentrations of oxygen in the water get too low fish and other aquatic animals that can’t escape can suffocate and die.

Excess phosphorus is a key driver of low levels of dissolved oxygen, which is why we closely monitor both parameters. Dissolved Oxygen wasn’t bad in September with only 6 sites failing to meet a healthy DO level of above 5.00 mg/L.

September Dissolved Oxygen Graph

September data for Dissolved Oxygen in mg/L.  The Neponset River experienced better than average DO levels this month with most sites meeting the goal of 5.00 mg/L.


Finally, we want to thank our dedicated volunteers for their participation over the past six months. We’re now in our 23rd year of monitoring the health of the Neponset River and couldn’t do it without their help.


Please note – October sampling results will be published next month. For more information about water quality data or volunteer opportunities, please contact Kelly Di Stefano at distefano@neponset.org


Kelly Di Stefano, Environmental Science Fellow, 25 October 2019

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